1. Field of the Invention
The present invention relates to a capacitor comprising a metal-deposited polyethylene 2,6-naphthalate film. More particularly, the present invention relates to a moist-heat resistant capacitor comprising a metal deposited polyethylene 2,6-naphthalate film which has improved adhesion between the film and the deposited metal.
2. Description of the Related Art
A polyester film a typical example of which is a polyethylene terephthalate film is used as a base film of a capacitor, since it is excellent in mechanical properties, heat resistance and electrical properties. With the recent progresses in various electric and electronic equipments, requirements for small-sizing and long-term reliability of the capacitor are becoming more stringent. Since an electrostatic capacity of the capacitor is inversely proportional to a thickness of a dielectric material, it is required to reduce the thickness of the base film so as to improve dielectric properties of the capacitor.
However, the conventionally used polyethylene terephthalate film cannot satisfy the requirement for the reduction of film thickness sufficiently. That is, since a very thin polyethylene terephthalate film has a very small strength per unit cross section of the film, it has poor workability or processability in the production step of capacitors including the vacuum deposition of metal.
To solve the above problem, attention is paid on a capacitor comprising, as a substrate film, a polyethylene 2,6-naphthalate film as disclosed in Japanese Patent Kokai Publication No. 136013/1987. In comparison with the polyethylene terephthalate film, the polyethylene 2,6-naphthalate film has poor adhesion to the deposited metal. When the capacitor comprising the polyethylene 2,6-naphthalate film is stored in a high temperature high humidity atmosphere, moisture penetrates in an interface between the base film and the deposited metal layer, so that the electrostatic capacity of the capacitor decreases with time. Accordingly, improvement of moist-heat resistance of the capacitor is highly desired to achieve good long-term stability.